1. Field of Invention
The present invention relates to the field of light-emitting diode (LED) lighting, and specifically to a drive circuit of an LED module.
2. Description of Related Arts
At present, light sources for street lighting include an incandescent lamp, a high pressure mercury lamp, a high pressure sodium lamp, a metal halide lamp, a fluorescent lamp, and the like. These street lamps generally have the following disadvantages: they are less environmentally friendly (mercury, lead, arsenic and other heavy metals contained therein are harmful to the environment), have high energy consumption and a short service life. Therefore, with the enhancement of global environmental protection consciousness, in countries throughout the world, especially in developed countries and regions, environmentally friendly lighting is more widely applied, and an environmentally-friendly light source will gradually substitute for these street lamps. An LED module with a 3-5V forward voltage is an environmentally friendly light source that has high efficiency, saves energy, and has a long luminescence lifetime, which is of great significance to environmental protection, energy saving, and protection of human health.
As known in the industry, adjustment of the brightness of the LED module with a 3-5V forward voltage is implemented by adjusting a current flowing through an LED, and therefore a brightness control for the LED is usually implemented by controlling an output current of an LED drive circuit. At present, in the field of LED drivers with a 3-5V forward voltage, products vary in quality. In order to reduce a cost, some products are provided with a simple line, have a power factor merely reaching about 0.5, and incur low luminous efficiency, thereby failing to meet a demand for efficient and energy-saving products in market; and in order to meet a high performance requirement, some products have a very complicated circuit. Refer to FIG. 1, which is a schematic diagram of a principle of a drive circuit of a conventional LED module with a 3-5V forward voltage. As shown in FIG. 1, a conventional LED drive power supply includes an electromagnetic interference (EMI) unit 121, an analog/digital (A/D) conversion unit 122, an input and output isolation unit 123, constant-voltage and constant-current output and overvoltage and overcurrent (an open circuit and a short circuit) protection unit 124, and a power factor correction (PFC) power supply 125, and the like. Because a large number of restrictive devices such as electrolytic capacitors and inductors are used in the above drive circuit, a line is rather complicated, it is difficult to lay a simple line, and the cost is greatly increased; furthermore, specific circuits of different products are also different and it is also highly difficult to develop a circuit, which increase development time; and because a part of the line of the drive power supply is complicated, a manufactured LED lamp is relatively large in size, which seriously affects an overall design of a lamp product and application flexibility thereof.
Among current LED lighting solutions, a direct current (DC) driving solution makes a manufacturing cost of LED lamps remain high all the time, because some elements are added in a multistage power conversion process; and in addition, an alternating current (AC) solution using discrete elements such as a resistor and a linear regulator reduces the cost, but incurs lower efficiency and a lower power factor. Therefore, how to provide a drive circuit of an LED module that supports AC direct input by using a high voltage solution and omits some elements that must be equipped in a DC solution is a problem to be solved urgently by practitioners in the art.